The objective of this project is to identify mechanisms which regulate placental steroid hormone production. Two enzymatic mechanisms potentially regulating estrogen synthesis have been proposed as a result of our studies with disrupted preparations of human placenta. A choriocarcinoma cell line in culture is being used as an intact cellular model to evaluate these and other mechanisms regulating estrogen production. Aspects evaluated include: relative activities of biosynthetic enzymes metabolizing conjugated and unconjugated estrogen precursors; enzyme inhibition; differential protein binding of conjugated and unconjugated estrogen precursors; effects of permeability and of cyclic AMP.